The present invention concerns a cooling plant of the type in which water is used as coolant, which can hereby be used either as cooled process water or as both primary and secondary coolant in closed cooling systems. Other application possibilities will be found in connection with heat-pump installations and the production of ice, which can be generated directly in the evaporator part of the plant. In such plants there is no need for separation surfaces in the evaporator and condenser units so that these units can be both inexpensive and highly effective. The plants can with advantage be used in cases where cold water at temperatures a few degrees above zero is required, e.g. at 5-10xc2x0 C. for cooling of e.g. processes and for air conditioning.
The plants work in accordance with the basic principle that the supply water, e.g. at a temperature of 10xc2x0-20xc2x0, is introduced into an evaporation chamber which is connected to the suction side of a steam compressor, which creates a strong vacuum in the chamber, e.g. in the order of 5-15 mBar, whereby the water expands while giving off a certain amount of steam which, despite a modest percentage of water, nevertheless represents such a high measure of evaporation heat that the residual water is significantly cooled, and it is therefore possible to achieve that the outlet water can be discharged at a temperature which is only approx. 0.5-1xc2x0 C. higher than the evaporation temperature.
As is the case with other coolants, there is effected a condensation of the coolant steam in a condenser which is cooled from outside, but with the present plant it also applies that work can be effected on the condenser side with immediate heat exchanging, i.e. condensation of the steam directly by means of water, so that both steam and water are introduced into one and the same condensation chamber. The steam is condensed in the cooling water so that this is heated, but again here it applies that the outlet water can be discharged with a temperature which is only approx. 0.1-1xc2x0 C. lower than the condensation temperature. The cooling water for the condenser is connected to an external cooling circuit via a cooling tower for cooling, for example from 25xc2x0 to 20xc2x0. The amount of water added from the condensate will thus be introduced directly into the circulating water from which, however, water will disappear by evaporation from the free surface in the cooling tower. Consequently, it must be noted that water must be operatively removed or added from or to this cooling circuit.
In principle, all this quite corresponds to more ordinary cooling plants with separate circuits for coolant and working medium. However, a considerable difference arises hereby in that there will constantly appear a content of non-condensable gas in the water, namely atmospheric air, which in a quite necessary manner must be removed to a degree which is sufficient to ensure that it does not interfere with the function of the plant. Air will arise in the supply water to the evaporation unit, but to an even greater degree in the supply water from the cooling tower to the condenser unit, where the water will be literally saturated with air. A related build-up of a distinct partial air pressure in the condenser will have a directly detrimental effect on the overall efficiency of the plant, primarily by increasing the condensation pressure against which the steam compressor must work, which results in a distinct increase in the consumption of energy.
It is in light of this that it is absolutely necessary and quite normal to arrange an effective separation of the air on the condenser side. This can naturally be effected directly via the associated vacuum pump, but because of a considerable content of steam in the air/steam mixture, this will demand an unrealistically large pump and a relatively great amount of energy. It is therefore well-known to insert a so-called NCG condenser (Non Condensable Gas) between the vacuum pump and the condenser chamber, into which NCG condensers there is constantly injected a certain smaller amount of the supply water to the main condenser, whereby there is brought about a part-condensation of that steam which is hereby sucked from the main condenser. The condensate is pumped out parallel with the discharge water from the main condenser, and the air/steam mixture, which via the vacuum pump must be compressed to atmospheric pressure, thus contains a reduced amount of steam.
In other connections it is known that alternatively there can be arranged a separate, preceding de-aeration of the water before this is injected into the condenser, namely by arranging a deaeration container above the condenser, the upper chamber of said container being connected with the necessary vacuum pump, and which during operation serves to receive the supply water for delivery to the condenser while maintaining the upper chamber in a state in which it is not filled with water. By the prevailing low pressure, there can occur a quite effective deaeration of the water from the widespread surface of the water in the container, so that the water introduced into to the condenser can be almost without any content of air. The sucking of the steam and residual air from the condenser can be effected via a connection from the condenser directly to the said upper chamber, in which a certain condensation of the steam will take place. Such pre-deaeration systems can be quite effective, but in this connection the known systems have a distinct disadvantage which will be discussed in the following.
In order to explain the invention, it is first required that the condenser itself is described in more detail. This traditionally involves a vacuum container which in principle is of simple construction and provided with a bottom outlet for water, and with one or more injection nozzles for the supply water, which must exchange energy with the steam from the steam compressor, in that the container also has an inlet opening for this steam. The container also has a discharge opening for the sucking out of the residual air and steam mixture via the already mentioned vacuum pump for maintaining a desired partial air pressure in the container. The injection nozzle(s) are configured with the object of providing a strong, spray-like jet of water, i.e. with fine droplets, which ensures a good exchange of heat with the generated steam, but also an almost total expulsion of the content of air in the water. Ideally, the air should remain in the water, so that they could be discharged together, but under the given conditions this will be a physical impossibility.
For the necessary comminution of the water through the use of the injection nozzles, a certain external over-pressure is required, for example of 0.6-0.9 bar. This is appropriate in that the supply water can be introduced at atmospheric pressure, e.g. from a cooling tower circuit, in that the necessary pressure difference will thus be brought about by the under pressure which prevails in the condenser chamber.
With the invention, the main object is to establish a cooling plant of the type in which work is effected with pre-aeration of the water, in that this potentially provides the best economy of the plant. However, there will hereby arise the aforementioned disadvantage with the pre-aerated systems, namely that work in the pre-aeration container must be effected at such a low pressure that the resulting over-pressure for the injection of water through the condenser""s nozzle system becomes completely inadequate. By a relevant known technique, though in another connection, this problem is solved by the pre-aeration container being physically placed at such a distinct height above the condenser that, in the connection down to this, there will arise a water column of such a height, typically in the order of 0.5-10 m, that despite the low pressure in the aeration unit there can still be established the necessary overpressure for an effective injection of water through the condenser""s injection nozzle(s).
However, this involves a highly inconvenient demand for a large overall construction height of the plant, and respectively considerable extra plant expenditure and significant constructional disadvantages. Use could be made of a separate pump for the building-up of the necessary injection pressure, but this would also involve extra installation and operational costs.
With the invention it has surprisingly proved that there is a possibility of working with a pre-aeration by using a pre-aeration container placed immediately above the condenser, namely by the condenser itself being modified in such a manner that the said injection nozzles can be dispensed with, while instead configuring the condenser with an upper distribution chamber which, down towards the condenser chamber, is limited by a sieve plate with a large number of perforations in the form of narrow holes or slots. Regardless of the water level, e.g. 25-200 mm, in the distribution chamber, by force of gravity the water will fall down into the condenser chamber in a large number of thin streams, which together have a very large surface area, and furthermore which are dissolved into small droplets after a quite modest fall height. In this way, the comminution of the water can be sufficient to achieve a quite effective exchange of heat in the condenser chamber, without the water having to be supplied at a high overpressure, and precisely therefore the pre-aeration container can be arranged directly over the condenser, i.e. with low total construction height.
According to the invention, this can be utilised with great advantage in that the pre-aerator is integrated directly with the condenser, namely merely in the form of one or more chambers formed in between sieve plates at the top of the vacuum container, which otherwise constitutes the condenser. Seen as a whole, this will be able to be configured as an integrated unit without any appreciable increase in construction height.
In that the said distribution chamber can stand under the same pressure as the condenser chamber, work can be effected with a common steam/air induction from both of these chambers, whereby the distribution chamber will appear as a functionally integrated part of the condenser, i.e. as a combined distribution and de-aeration chamber. It is possible, however, by a serial suction from the condenser chamber to the distribution chamber, and from here to the vacuum pump, to achieve a certain part-condensation of the steam fraction in the distribution chamber, whereby this chamber can work with a real pre-aeration effect.
An additional pre-aeration chamber can, however, be established in a very simple manner as an immediately overlying chamber between a sieve plate which forms the top in the distribution chamber, and an overlying sieve plate which forms the bottom in an upper distribution chamber. In the upper pre-aeration chamber there will thus also be supplied water in a large number of down-falling, thin streams, from which despite a modest fall height there can still be extracted a very large part of the air content, and here there can thus be effected a considerable air separation at a higher pressure level than by the condenser pressure, i.e. a real pre-aeration at a pressure from which distinctly less energy is required to compress the air fraction to atmospheric pressure.
There can hereby with advantage be arranged a beneficial two- or multi-stage aeration of the water. The suction from the individual de-aeration stages can be connected via an air-concentration unit and a pump to the next, physically overlying pre-de-aeration stage, so that a stepwise concentration and compression of the air is achieved. The pump from the last stage compresses the air up to atmospheric pressure. For effective concentration of air in the individual air-concentration units, it has been found especially advantageous and simple to take a quite small part-stream of relatively cold water, preferably from the evaporator outlet, which by spraying-out in the air concentration units some of the steam is condensed from the sucked-off mixture of air and steam, i.e. a lowering of the steam""s partial pressure.
It is hereby possible to work with absolutely minimised pump equipment for de-aeration of the water.
As far as the effect of the actual condenser is concerned, with the invention it has been ascertained that a significant improvement can be achieved by mounting a jet/droplet-breaking insert, e.g. in the form of a simple net material, in the condenser chamber. When the net mesh is of the same size as the thickness of the water jets/droplets, there will hereby arise such a decomposition of these that they are shattered by the otherwise unhindered passage through the net, so that under the net there is formed a spray-like cloud of fine droplets, which even with a relatively short fall height can effect a distinct extra contribution to the exchange of heat. It has been found that this effect is best achieved when the net is arranged at the level where the jets of water have just changed to droplet form. In that the heat exchange can already be good enough, the addition of the net instead can be used to reduce the fall height of the droplets, so that an effective/compact condenser with a further reduced construction height can be achieved.
Also where the evaporator is concerned, though to a lesser degree, it is relevant to arrange a deaeration of the supply water, and also here work can with advantage be effected in accordance with quite the same principles, so that the evaporator with associated pre-deaeration chamber can also be configured in a fully integrated manner.
The invention will thus make it possible to build a cooling machine of the type discussed in a very compact configuration with low construction height, and rendered cheaper both by the beneficial integration of air separators in the evaporator- and condenser-containers themselves, and by the simplified pump equipment for effecting the necessary air separation.